The processing of fish and marine arthropods, such as shrimp, crab and crayfish, produces large quantities of marine by-products. Most are used in low end products such as fertilizers, fish silage or pet food but the unused by-products pose an economic burden for the marine product processing industries because of the need to dispose of such residues in an environmentally sound way. By some estimates such by-products represent 25% of the total production captured by fisheries.
For example, during the processing of shrimp for its subsequent freezing and marketing, a large amount of remains are generated since 35% of the animal is inedible and must be discarded. These remnants or by-products are composed of the shrimp's cephalothorax and exoskeleton. However, these shrimp by-products are rich in high-value substances, such as chitin, protein, lipids, carotenoid pigments (astaxanthine) and minerals. The majority of the inedible by-products are disposed at landfills or dumped back into the ocean, thus causing serious environmental problems and considerable losses to the shrimp processing industry. At present, only a small amount of these by-products are used as a supplement for animal feed.
The most common technique for shrimp by-product utilization is sun drying. This technique has low hygienic control and the products are used primarily for animal consumption. Other methods employ chemical acids and alkalis at different concentrations, temperatures and times for the extraction of chitin and recovery of protein hydrolysates. However, these methods cause a depolymerization and partial deacetylation of the chitin. Moreover, these methods complicate the recovery of other products, such as protein and pigment.
Enzymatic methods have been developed for the extraction of chitin, liquid hydrolysates and pigments. Such methods use enzymatic extracts or enzyme isolates. Other studies have reported the use of microbial enzymes, such as commercial alcalase, for the extraction of proteins from shrimp and marine animal by-products. The combination of alcalase and pancreatin has been reported for the extraction of chitin, hydrolyzed protein and pigmented lipids.
Lactic fermentation processes have been used as a substitute for the above chemical and enzymatic processes. Fermentation represents a cost effective technique which stabilizes and retains the nutritional quality of the by-products. The optimal conditions for fermentation depend on several factors including the choice and concentration of carbohydrates, pH, temperature, time, and the choice of aerobic or anaerobic conditions. Another important factor is the choice of microorganism and initial inoculum concentration. To facilitate the fermentation process of shrimp by-products pure cultures of lactic acid bacteria (LAB) have been used. Such LAB include Lactobacillus plantarum (Rao, M. S., Stevens, W. F., 2006, “Fermentation of shrimp biowaste under different salt concentrations with amylolytic and non-amylolitic Lactobacillus strains for chitin production,” Food Technology and Biotechnology 44, 83-87; Rao, M. S., Muñoz, J., Stevens, W. F., 2000, “Critical factors in chitin production by fermentation of shrimp biowaste,” Applied Microbiology and Biotechnology 54, 808-813; Bhaskar, N., Suresh, P. V., Sakhare, P. Z., Sachindra, N. M., 2007, “Shrimp biowaste fermentation with Pediococcus acidolactici CFR2182: optimization of fermentation conditions by response surface methodology and effect of optimized conditions on deproteination/demineralization and carotenoid recovery,” Enzyme and Microbial Technology 40, 1427-1434), Lactobacillus sp. B2 (Circ, L. A., Huerta, S., Hal, G. M., Shirai, K., 2002, “Pilot scale lactic acid fermentation of shrimp waste for chitin recovery,” Process Biochemistry 37, 1359-1366; Shirai, K., Guerrero, I., Huerta, S., Saucedo, G., Castillo, A., Gonzalez, R. O., Hall, G. M., 2001, “Effect of initial glucose concentration and inoculation level of lactic acid bacteria in shrimp waste ensilation,” Enzyme and Microbial Technology 28, 446-452), Lactobacillus casei (Shirai 2001), Lactobacillus paracasei (Jung, W. J., Jo, G. H., Kuk, J. H., Kim, Y. J., Oh, K. T., Park, R. D., 2007, “Production of chitin from red crab shell waste by successive fermentation with Lactobacillus paracasei KCTC-3074 and Serratia marcescens FS-3,” Carbohydrate Polymers 68, 746-750), Lactobacillus pentosus (Bautista, J., Jover, M., Gutierrez, J. F., Corpas, R., Cremades, O., Fontiveros, E., Iglesias, F., Vega, J., 2001, “Preparation of crayfish chitin by in situ lactic acid production,” Process Biochemistry 37, 229-234; Shirai 2001), Lactobacillus acidophilus B4495 and Lactobacillus lactis (Bhaskar 2007), Lactobacillus salvarus (Beaney 2005), Enteroccus facium (Beaney 2005), Pedioccoccus acidilactici (Bhaskar 2007) and Pedioccoccus sp. L1/2 (Choorit, W., Patthanamanee, W., Manurakchinakorn, S., 2008, “Use of response surface method for the determination of demineralization efficiency in fermented shrimp shells,” Biores. Technol. 99, 6168-6173). In addition, a mixture of four LAB has been used (Bhaskar 2007) and there are reports using Lactobacillus in combination with Serratia marcescens FS-3 (Jung 2007) or Staphylococcus carnosus (Shirai 2001). However, the industrialization of such fermentation processes has not been successful due the poor performance of commercial inoculants.
Lactic fermentation of shrimp by-products produces protein hydrolysates, chitin, minerals, and lipids. Chitin and its deacetylated derivatives have many applications in agriculture, biomedicine, food and the paper industry, while liquid hydrolysate is an excellent source of essential amino acids that can be used for human or animal consumption. The lipidic paste contains sterols, vitamin A and E, and carotenoid pigments such as astaxanthin which can be used in feed for salmonoids or as a natural coloring in the food industry.
Chitin is a natural polysaccharide found particularly in the exoskeleton of crustaceans, the cuticles of insects, and the cell walls of fungi. Because chitin is one of the most abundant biopolymers, much interest has been paid to its biomedical, biotechnological and industrial applications. Chitosans are poly-(β-1-4)-N-acetyl-D-glucosamine compounds produced by the deacetylation of chitin (β-1-4)-N-acetyl-D-glucosamine. Glucosamine is an amino monosaccharide obtained by de-polymerization of chitosan. It participates in the constitution of glycosaminoglycans, a major class of extracellular complex polysaccharides. Glucosamine sulphate, glucosamine hydrochloride and N-acetyl-glucosamine are commonly used alone or as part of a mixture.
Generally, the liquid hydrolysate has a high content of essential amino acids, indicating a high nutritional value that justifies its use as a supplement for animal and aquaculture nutrition or as a nitrogen source in growth media for microorganisms. Additionally, these hydrolysates are a source of free amino acids and can be used for nutrition in plants as a biostimulant.
Astaxanthine (3,3′-dihydroxy-β,β-carotene-4,4′-dione), a ketocarotenoid oxidized from β-carotene, naturally occurs in a wide variety of marine and aquatic organisms. Due to its attractive pink color, its biological functions as a vitamin A precursor, and antioxidative activity, astaxanthine can be used as a colorant in food and in medicine. In the structure of astaxanthine, two identical asymmetric carbon atoms at C3 and C3′ are found. However trans-asthaxanthine is the quantitatively most prevalent carotenoid in crustacean species.
References disclosing these and other products from lactic fermentation include: Sanchez-Machado et al. “Quantification of organic acids in fermented shrimp waste by HPLC” Food Technology and Biotechnology, volume 46, 456 (2008); Sanchez-Machado et al. “High-performance liquid chromatography with fluorescence detection for quantitation of tryptophan and tyrosine in a shrimp waste protein concentrate”, Journal of Chromatography B, volume 863, 88 (2008); Lopez-Cervantes et al., “Quantitation of glucosamine from shrimp waste using HPLC” Journal of Chromatographic Science, volume 45, 1 (2007); Lopez-Cervantes et al., “Quantification of astaxanthin in shrimp waste hydrolysate by HPLC” Biomedical Chromatography, volume 20, 981 (2006); Lopez-Cervantes et al., “High-performance liquid chromatography method for the simultaneous quantification of retinol, alpha-tocopherol, and cholesterol in shrimp waste hydrolysate” Journal of Chromatography A, volume 1105, 1-2 (2006); Lopez-Cervantes et al., “Analysis of free amino acids in fermented shrimp waste by high-performance liquid chromatography”, Journal of Chromatography A, volume 1105, 1 (2006).